EFFECT OF PREPARATION METHOD ON THE PROPERTIES OF NB2O5 PROMOTED PLATINUM CATALYSTS

Pt/Nb2O5 catalysts were prepared on a reducible support by ion exchang e and incipient wetness of different platinum salts. The Pt/Nb2O5/Al2O 3 catalysts were prepared with several loading of niobium oxide over a lumina, aiming different surface coverages and platinum dispersions. T hese catalysts were characterized by using different techniques: TPR, DRS, chemisorption of H-2, CO, CO2 and pyridine. The catalytic activit y was evaluated in the n-heptane conversion. Platinum oxide was the ma in surface, precursor on the Nb2O5 supported catalysts, while a oxychl oroplatinum surface complex was the precursor for Pt/Nb2O5/Al2O3 catal ysts. These different precursors promote the formation of different pl atinum particle sizes, being the Pt/Nb2O5/Al2O3 samples more disperse. After high temperature of reduction, the platinum adsorption capacity decrease on all the samples, due to the reduction of Nb2O5, and subse quent blocking of surface platinum atoms. Nb2O5 and Nb2O5/Al2O3 suppor ted catalysts are very selective to olefins in the n-heptane conversio n. Furthermore, Bronsted acidic sites an formed on Pt/Nb2O5/Al2O3 cata lysts with higher Nb2O5 loading, leading to a better stability of the catalysts. (C) 1998 Elsevier Science B.V. All rights reserved.